Memory-monitor for Mac.

content/browser/memory/memory_monitor_mac.cc

+// Copyright (c) 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "content/browser/memory/memory_monitor_mac.h"
+
+#include <sys/sysctl.h>
+
+#include "base/memory/ptr_util.h"
+#include "base/process/process_metrics.h"
+
+namespace content {
+
+namespace {
+
+// The number of bits to shift to convert KiB to MiB.
+const int kShiftKiBtoMiB = 10;
+
+}  // namespace
+
+MemoryMonitorMac::MemoryMonitorMac(MemoryMonitorDelegate* delegate)
+    : delegate_(delegate), critical_free_mb_(0) {}
+
+MemoryMonitorMac::~MemoryMonitorMac() {}
+
+int MemoryMonitorMac::GetFreeMemoryUntilCriticalMB() {
+  // Get the amount of free memory in the system. The "free" amount is a poor
+  // indication because it doesn't take into consideration memory that is
+  // in use but can be easily freed, such as disk buffers.
+  base::SystemMemoryInfoKB mem_info = {};
+  delegate_->GetSystemMemoryInfo(&mem_info);
+  int free_mem = mem_info.free >> kShiftKiBtoMiB;
+
+  // Get the current system memory pressure.
+  int mac_memory_pressure;
+  bool success = delegate_->GetSystemMemoryPressure(&mac_memory_pressure);
+  DCHECK(success);
+
+  // Adjust the "critical threshold" according to current memory pressure.
+  switch (mac_memory_pressure) {
+    case DISPATCH_MEMORYPRESSURE_NORMAL:
+      // Under normal operation, allow more and more memory to be used.
+      if (critical_free_mb_ > 0)
+        --critical_free_mb_;
+      break;
+    case DISPATCH_MEMORYPRESSURE_WARN: {
+      // Once free memory starts to get low, gradually reduce the amount
+      // of memory that con be used.

[shrike, 2016/09/29 22:48:43]

"con" should be "can"

+      int half_free = free_mem >> 1;
+      if (critical_free_mb_ < half_free)
+        critical_free_mb_ = half_free;
+      else
+        ++critical_free_mb_;
+    } break;
+    case DISPATCH_MEMORYPRESSURE_CRITICAL:
+      // When memory pressure is critical, assume that system is about to swap.
+      critical_free_mb_ = free_mem;
+      break;
+  }
+
+  // Return the amount of memory until critical.
+  return free_mem - critical_free_mb_;
+}
+
+// static
+std::unique_ptr<MemoryMonitorMac> MemoryMonitorMac::Create(
+    MemoryMonitorDelegate* delegate) {
+  return base::MakeUnique<MemoryMonitorMac>(delegate);
+}
+
+// Implementation of factory function defined in memory_monitor.h.
+std::unique_ptr<MemoryMonitor> CreateMemoryMonitor() {
+  return MemoryMonitorMac::Create(MemoryMonitorMacDelegate::GetInstance());
+}
+
+MemoryMonitorMacDelegate* MemoryMonitorMacDelegate::GetInstance() {
+  return base::Singleton<
+      MemoryMonitorMacDelegate,
+      base::LeakySingletonTraits<MemoryMonitorMacDelegate>>::get();
+}
+
+bool MemoryMonitorMacDelegate::GetSystemMemoryPressure(int* mem_pressure) {
+  size_t length = sizeof(*mem_pressure);
+  sysctlbyname("kern.memorystatus_vm_pressure_level", mem_pressure, &length,
+               nullptr, 0);
+  return true;
+}
+
+}  // namespace content